Conventionally, there has been practically used a lash adjuster that automatically adjusts a valve clearance provided between an intake or exhaust valve and a cylinder head of an internal combustion engine to substantially zero. With such a sealed type lash adjuster, in the aspect of function, clatter noise generated by interference between the intake or exhaust valve and the cylinder head is eliminated by means of this lash adjuster. Moreover, in the aspect of maintenance, it becomes unnecessary to perform operation for periodically checking and adjusting the valve clearance. The lash adjuster includes, for example, an external oil feed type lash adjuster that utilizes engine oil. In the case of this external oil feed type lash adjuster, if a filled quantity of the engine oil is inappropriate or if degraded oil continues to be used, a risk that air or foreign substance is mixed into the oil increases. Therefore, as a result of these factors, the function of the lash adjuster can be impaired. That is, in the external oil feed type lash adjuster, the function of the lash adjuster depends on whether the engine oil is well maintained or not. On the other hand, the lash adjuster includes a sealed type lash adjuster in which a liquid such as oil is hermetically enclosed. With such a sealed type lash adjuster as just described, the above-described factors impairing the function thereof can be eliminated.
With regard to the sealed type lash adjuster, a sealed type lash adjuster such as shown below has been proposed, for example, in Patent Document 1. The sealed type lash adjuster proposed by Patent Document 1 is equipped with an oil seal having two lips in an X-letter shaped cross section (hereinafter simply called X-seal) between a body and a plunger. This X-seal can seal two liquids on both sides of the seal at the same time. Consequently, this sealed type lash adjuster has a structure to simultaneously prevent outflow of the oil sealed by the X-seal to the outside and intrusion of the engine oil from the outside.
[Patent Document 1]
    Japanese Examined Patent Publication No. JP-B-62-029605